It is often necessary to replace malfunctioning heart valves within the body. Heart valve replacement generally has been accomplished by a major open heart surgical procedure, requiring general anesthesia, full cardiopulmonary bypass with complete cessation of cardiopulmonary activity, seven to ten days of hospitalization and months of recuperation time. The mortality rate with this type of procedure is about five to six percent.
Endovascular procedures for valve replacement provide an alternative to open heart surgery. For example, in patients with serious aortic valve disease who are too compromised to tolerate open heart surgery, surgeons have used endovascular balloon aortic valvuloplasty. This procedure involves use of endovascular balloon dilatation to split commissures in diseased aortic valves with commissural fusion and to crack calcific plaques in calcified stenotic aortic valves. This method provides only partial and temporary relief for a patient with a stenotic aortic valve. A repeat procedure within a year of the first procedure is often required.
An alternative treatment regimen is endovascular valve supplantation. In this procedure, instruments are used to insert a mechanical valve in the lumen of a central blood vessel via entry through a distal artery, for example, the brachial or femoral artery. The descriptive terms distal and proximal, when used in relation to the vasculature in this application, refer to directions further and closer from the valve replacement or procedure site, as applicable. A guide wire is placed through the entry vessel and fluoroscopically directed to the desired situs. Flexible catheters are then guided over the guide wires which are used to propel and direct the new valve through the blood vessel to the desired central location near to the malfunctioning heart valve where it supplants the function of the existing valve.
Endovascular heart procedures, in contrast to open heart surgical procedures, would require only local anesthesia, partial or no cardiac bypass, one to two days hospitalization, and should have a reduced mortality rate as compared to open heart procedures. However, as discussed in the literature but never actually practiced, endovascular heart valve supplantation is limited to supra-annular arterial based mechanical valves which require an elongated mounting catheter originating at the distal arterial entry point to maintain the position of the valve in the aorta and therefore does not provide a permanent or internalized system. Valve supplantation is also limited to treating regurgitant aortic valves and is not applicable to stenotic aortic valves or any other malfunctioning heart valves. In addition, once implanted, mechanical valves predispose the patient to thrombus formation and emboli, mandating long term anticoagulant therapy; intracranial hemorrhages are a serious side effect of long term anticoagulant therapy.
A potential alternative to a mechanical valve is a bioprosthetic valve. A bioprosthetic valve can be either a homograft (a fresh human), allograft (a fixed human) or a xenograft (a fixed other species) valve. Homograft valves, in contrast to xenograft valves, are rarely used because of the lack of access to fresh human valves. Porcine glutaraldehyde preserved valves are often used since they are readily accessible and storable and are available in a variety of sizes. Bioprosthetic valve replacement does not predispose a patient to thrombus formation or emboli, and, therefore, requires no long-term anticoagulant therapy. Bioprosthetic valves are presently a mainstay in aortic valve replacement. Bioprosthetic heart valve replacement is preferable in patients who cannot tolerate long-term anticoagulant therapy or are otherwise potentially noncompliant with a long term medical regime.
To date, bioprosthetic and mechanical valves have been inserted near or at the native annulus site through open heart surgery and except for the Magovern-Cromie Valve which used pins to fix the valves have required sutures for fixation at the insertion site; means for endovascular valve replacement with any valve are not available. It would therefore be of interest to provide a endovascular means i) to easily remove a dysfunctional natural or prosthetic valve and ii) to replace the dysfunctional valve with a endovascularly replaceable bioprosthetic or flexible synthetic valve, independently fixed without sutures or catheter, near or at the native valve annulus site.
Relevant Literature
U.S. Pat. No. 3,671,979 to Moulopoulos, issued Jun. 27, 1972, describes a endovascularly inserted conical shaped umbrella-like valve positioned and held in place by an elongated mounting catheter at a supra-annular site to the aortic valve in a nearby arterial vessel. The conical end points toward the malfunctioning aortic valve and the umbrella's distal ends open up against the aorta wall with reverse blood flow, thereby preventing regurgitation.
U.S. Pat. No. 4,056,854 to Boretos, issued Nov. 8, 1977, describes a endovascularly inserted, catheter mounted, supra-annular valve in which the circular frame abuts the wall of the artery and attached flaps of flexible membrane extend distally in the vasculature. The flaps lie against the artery wall during forward flow, and close inward towards the central catheter to prevent regurgitation during reverse blood flow. The Boretos valve was designed to be positioned against the artery wall during forward flow, as compared to the mid-center position of the Moulopoulos valve, to reduce the stagnation of blood flow and consequent thrombus and embolic formation expected from a valve at mid-center position.
Reviews relating to replacement valves include: Gibbon's Surgery of the Chest, 5th Ed., David C. Sabiston, Jr., M.D., Frank D. Spencer, M.D., 1990, Vol. II, Ch. 52, pp. 1566-1596, and Textbook of Interventional Cardiology, Eric J. Topol, 1990, Chs. 43-44, pp. 831-867.